More inlet cam duration on a turbocharged engine

[turbotoaster]

Hi guys,

Wanted to know your thoughts on this, assuming both cams have the same value of lift, on a turbocharged engine, moving from a 260 degree duration intake and exhaust cam to a 274 degree intake but keeping the 260 exhaust, would I see any gains in power across the rev range.

My thoughts were unless your revving the engine fairly hard(7500rpm+) then not fitting the 274 cam on the exhaust side is a good idea due to lower rpm power loss and not really getting alot at the top end due to turbine exhaust gas restriction.

But having a larger duration on the inlet cam will help get the air into the cylinder assuming you can control the cam timing to avoid to much overlap.

I notice with cosworth engines some people go for more aggressive intake cam and see more power so I was wondering if it was down to this

Can anyone who knows cams with turbocharged applications help at all.

I can provide information on the engine im using if it helps

[turbotoaster]

1800 capacity Rover K series twin cam head

80mm bore

89.3 stroke

circa 130cfm head (vvc head with ported inlet/exhaust and standard sized 31.5/27.5 valves)

9:1 wossner pistons

balanced components

currently

49/60mm billet compressor wheel(turbo builder tells me it will flow 40lbs maxed out), 49/65mm turbine wheel, 0.48 cosworth t3 turbine housing, 3" short exhaust.

currently piper 262 degree cams with 9.65mm lift on inlet and exhaust.

Looking for a powerband from 4000-7500rpm with 8000rpm rev limit, the car will be raced on track, has a shortish ratio gearbox, only weighs 700kg so dont need lots of low down torque, ideally making 410bhp.


Here below is a dyno graph from last time i stuck it on a dyno, this is with 19psi of boost

This is with a stock OEM bottom end, no forged bits and a stock port vvc head but piper cams(circa 110cfm)

Makes circa 345bhp at 22psi of boost based on AFR vs INJ duty

Please ignore the red lines, those are a supercharged honda engine.



As you can see it comes on aggressive torque wise from the turbo and then dies after 6000rpm

One thing I did wonder about is im on stock valve springs, is there a way of knowing if they are reaching the limit(its common on LS1 engines you need to uprate the springs when turbo'd)

Does this help at all?

[turbotoaster]

Evoluzione said:

To answer your initial question I wouldn't bother changing the cam with that spec, it's probably already working as well as it all could and a longer duration inlet cam won't give you much.
I would say your .48 housing is too small (journal bearing turbo?), but there isn't enough data there to make a precise decision on cams. You need incremental port flows (what is a 130cfm head exactly?) for both in and ex and you also need to log your ex back pressure as you may find that it's a bit on the high side. The figures at the bottom of your graph are unreadable too.

Valve springs not only need to be strong enough, but also they don't want to be going coilbound at full valve lift (which is a bit low on your inlet).
With the correct set up something like a 276/11.5mm with 2mm of lift at TDC ex 276/10mm 1mm lift at TDC will see early spool, good mid range and top end, but everything else needs to be optimised to be able to work with a pair of cams like that.

Ive got the option of choosing the piper285h cam which is 274/11mm with 2.24mm of lift at TDC for the inlet cam and keeping my piper270h which is 264/9.65 with 1.27mm of lift at tdc for my exhaust cam.......this seems fairly close to what you have mentioned apart from the extra duration on the exhaust side.

From my understanding the more lift the better, but I wasnt sure if the extra duration on the inlet side would more than offset that via overlap.

Would that duration on the exhaust side be ok for the powerband im after?


Ive already been trying for ages to find a 0.63 rear housing as I wondered at which point the housing becomes a restriction, it seems its nearly impossible to find, even contacted turbotechnics who cast new ones and they wouldnt sell me one, I do have the option of increasing the turbine wheel circa 6% to try and help, but wasnt sure if the ultimate restriction was the wheel, or the housing itself, my thoughts are its the housing but I dont really want to change the entire turbo if I can help it.

yes its a journal bearing turbo.

head info

correct to 10" both sides
130 inlet at 11mm of lift
125 inlet at 9.65mm of lift

90 exhaust at 9.65mm of lift

These figures arnt exact as there is a little bit of guesswork involved from looking at data of ported heads comparable to mine.

Earlier on today I was reading a review on turbo cams by a company called AMS and they mentioned looking at EBP effects cam overlap choice to stop reversion, I have read that people have added a fitting onto the manifold, connected a steel line and run it to the dash by which time its cooled enough to be fitted to a normal boost gauge, i dont know if it would cool enough though as ive never tried it.

According to piper you can run up to 11mm of lift on stock valve springs in a NA format, going over to turbo, I didnt know if that would make a significant difference is it does on the LS engines.

I had never really imagined the engine would be making the power it does without popping, especially as I do my own mapping, but since its going well I may aswell keeping pushing on.

With regard to the graph, sorry about that, it starts at 2500 and goes up in 500rpm, peak torque is 4750rpm and then falls like a stone, power is 6000rpm, the power stops at 7250rpm

[turbotoaster]

Hi Dave, your talking about steves car, yes ive followed his build very closely and his higher duration cams didnt seem to suit the engine even with the high revs, but i wondered if that was because the higher duration on the exhaust cam was causing to much reversion in the mid range?

How much difference is there flow wise between his current ported head(none vvc) and a stock vvc?

I spoke to Kent cams at autosport show and they would be willing to make me 265 degree with 11.5mm of lift which sounds like the best of both worlds, or maybe 11mm if i wanted to keep the stock hydraulics.

What I am trying to work out though is why the torque falls like a stone so badly after 4750rpm, do you think it might be because its a stock port/valve vvc head, the boost doesnt drop off, will the ported head improve this or will top end always be dictated by turbo?

Would you think there is anything on the engine you would do, or would you point it at the turbo side.

Also its running on a turbotechnics plenum, which has a fairly large plenum volume with a 52mm throttle body, i now have a 56mm throttle body for it aswell as a set of direct to head throttle bodies to maybe try in the future

[turbotoaster]

Evoluzione said:

Yes a cam like that would suit your power band, but only if the other components matched it.
I'm unsure why a completely different engine has been brought up, you might aswell compare an apple with an orange, it's of no relevance to this thread and your engine whatsoever.

ok well thats good news to hear, not sure whether to just put the head on and run it, then add the inlet cam after so i can see if theres any improvement, I suppose that would be the sensible thing to do rather than adding both.

Sorry about the LS thing, just the valve spring part was interesting and I didnt know if maybe thats why my power is dropping at the top.

What do you think about the larger exhaust wheel vs turbine housing?

[turbotoaster]

Evoluzione said:

Small cam - small turbo.

I think you're flogging a dead horse with that turbo really, things have come a long long way since that was designed in the 80s, that's why you can't find a housing for it. The cams I outlined (or something similar) are for a thoroughly modernised engine, you can't really run lots of overlap and duration with a restrictive ex port, log manifold and old turbo. The exhaust gasses won't be able to get out as well as they should be able to resulting in back pressure, pumping losses, reversion and even some waste gas left in the cylinder. It needs the opposite of that including a modern turbo which will spool easily and produce less back pressure. It isn't just down to housing and wheel size, but bearings, trim and the design of the vanes which also contribute.

Take a look at the graph below, it has the same stroke and CR as yours, but bigger bore (2ltr) and a much bigger turbo (GT35) the cams in that had a lot of duration and overlap, but look what it's done to the curve and how early (and violently) the turbo wakes up. Traditional (N/A) thinking would say it's going to be an engine with a very high rpm powerband, but it isn't, it's very broad. Don't be fooled by the drop off or levelling off of the curves, that was because it had hit the upper limit of the map sensor so the boost was being artificially held back when really it had enough in it to carry on climbing from 5800 onwards.



If that was in a 2wd it would need the boost reigning in in the lower gears, but it was 4wd so when it spooled it gripped and was like being smote towards the horizon by the hand of God on a bad day, it made your neck ache within minutes just from holding your head upright.

The one below is much lower spec and a GT3076R, but still the spool and power band aren't bad.



They didn't get like that by accident, they were designed from scratch to deliver what they did and every single piece was a known quantity, I still know now the tolerance on the bores, the crank journal size and bearing clearance, the port flows at every 1mm of lift, the ex and in runner diameter and length etc. There was no guessing, no risks taken.

Comparison of an OE valve spring with a race spec one:



The engine builder didn't think to check, it resulted in this:

Thats one of the biggest issues between yourself and me is that im just learning as I go along, im no pro engine builder so there may be things that are working against each other in my build but i dont have the knowledge to realise it.

I know you mentioned its an old turbo, my concern about running a bigger turbo was when i first got it together I used an ebay t3/4.63, which is wheel sizes is circa a cosworth T4, looking at the wheels pretty much matched a gt3076 so yes a laggy old girl, but with that turbo it took 7000rpm till i hit 16psi of boost so my fear is that if I keep going larger I am not going to be able to spool the turbo, would you suggest a gtx3067 maybe as the compressor wheel isnt to big yet it has a decent sized rear wheel to reduce EBP and use the cams to increase airflow to help spool it?

I do run a tubular manifold rather than a log

While my new head should flow circa 15% better than my stock one, as far as I aware that will only really come into play at higher rpm when the stock head was reaching its restriction anyway, even with the porting they arnt big ports, i think around 36mm inlet and exhaust so that might be a restriction to its overall flow capacity, probably flow circa 25% less flow than your ported head which is alot, so wont be able to spool turbos like you do, or are you saying its purely down to engine capacity and head flow doesnt effect spool?

Edited by turbotoaster on Tuesday 2nd February 01:02

[turbotoaster]

stevieturbo said:

I can't imagine standard valve springs are in any way a good idea for such a build ? Unless they're well known for being capable with the extra lift and pressures.

Do you have vernier wheels ? Can you spend a little dyno time playing with cam timing to see if that will help you any ?

And/or switch to a better turbo, one of the smaller Borg Warner EFR's is bound to be a night and day difference to that old unit.

Or ATP are offering these for the Ecoboost, smaller engine so should be comparable ?

400hp capable unit

http://www.atpturbo.com/mm5/merchant.mvc?Screen=PR...

Or bare 2860 billet core for a normal generic fitment, needs T25 housing.

http://www.atpturbo.com/mm5/merchant.mvc?Screen=PR...

And you mention VVC, what actual control do you have over valve timing ?

According to DVAndrews, in NA application the stock valve springs on 9.6mm lift cams are ok to 7500rpm, after that they need changing.......i dont know if the pressures from turbocharging will dramatically reduce that rpm point where issues occur?

If i was going for the 11mm lift inlet cam i would replace them all with double valve springs.

Yes I have verniers, playing with that is something I havent really got around to doing yet, the cams are solid and cannot be electronically adjusted, with rover k series you just use the head that used to run vvc because of much better ports and bigger valves......i suppose in theory you could get piper to make a replacement vvc cam with lots of lift and then control the timing it with the electric system.

The manifold I had a friend make for me is pretty basic, its not twin scroll, I never thought to make it that way at the time as i was only after 220bhp from the engine, its only when i put it on the dyno after road tuning and it made 285bhp on a small turbo that I realised there is a bit of potential with this engine.



Just looking at the EFR turbos now, I could buy a t3 to v band adapter and maybe go for 6758 with a v band inlet, that would get me to 400bhp at circa 1.5bar maybe, the 6258 might be getting maxed out at 2.0bar.

Saying that, realistically I would be happy with 400bhp i think as the car only weighs 700kg, its probably me getting greedy thinking when its forged i might start chasing 450bhp so i can go play at santa pod rather than track use its currently for

[turbotoaster]

chuntington101 said:

Are there any more details of this car out there on the interweb?

http://forums.seloc.org/viewthread.php?tid=241615

you will need to register to view it

Evoluzione said:

Whilst the B&W are possibly the best out there at the moment, there is the GTX28 too maybe? Just thinking at least if he stays with the Garrett family and T3 then it saves on changing the fittings and sometimes they can be had for a bit less money.

I see that ATP in the US sell t3 housings for this turbo, easy to get in the UK? doesnt this just mean im still running a relatively small turbine wheel and hence highish EBP or will the 0.63 offset that

[turbotoaster]

Evoluzione said:

I'm not sure you are learning, you are picking at other peoples knowledge base and even then you aren't really reading it properly and just bolting on one random part after another.
Go back to my very first post and read it carefully, then apply it to what you have done by simply swapping one turbo for another.
You have the same resources available to you as anyone else does (including me), that includes books, compressor maps and to some degree, technical forums. I suggest sitting down and reading them. Tedious I know, but you'll educate yourself, save time, money and stand a good chance of wheeling something out of the shed that works properly.

Once you've been pointed in the general direction you will have to do some actual work yourself!

What is working in your favour is (hopefully) you've built a strong bottom end, you have 9:1 CR and a long stroke. These work well with a longer duration cam - just make sure you have enough piston/valve clearance if you do any cam swaps....

Edited by Evoluzione on Tuesday 2nd February 13:42

Your right, I wasnt learning, i was just trying to pick bits of info out of it to use.

you mention in your first big post the turbo isnt big enough overall for the power that im now looking for, so all the additional information ive added isnt really going to change that fact.

I have been looking online at the moment to see the best way to connect into the manifold to measure EBP as you need something that you can easily block off after, might go and see pirtek local and see what they would recommend, im guessing something like a oil braided line with screw on fitting on the manifold itself. I will do some more research to see what pressure ratio is to high vs whats ideal, that might teach me how big i need to go on the turbine side to give the best overall power band.

Stevieturbo, since i have a ported head in pieces, the £180 for double valve springs makes sense to put them in now and will cover for the future if i want to go bigger cams

Thanks for both of your help, as you both say, until i know the EBP im purely guessing what the issue could be.

[turbotoaster]

Evoluzione said:

Yes the amount of air you quoted that your turbo will supply is more likely to give a 360 bhp and that is pushing it a bit.
Can you get me some more dimensions? What does your intake manifold look like?

Dont any more about the turbo in terms of dimensions than what I stated, what extra info do you need, the guy who built it for me told me hes had the turbo make 400bhp at 30psi on cosworth with a 0.63 turbine housing, so i was expecting with the 0.48 to maz circa 370bhp, but hold nice power to 7000rpm, saying that it could be cam timing that needs work.

here is a couple pictures of my current intake manifold, its now got a 56mm throttle body but had a 52mm one when it was last running.

The upper plenum is a turbotechnics cast version that is larger than the factory one, no trumpets or anything fancy inside